Position rack in center of oven and preheat to 400 degrees. Rub a 2 quart shallow gratin dish with 1/2 teaspoon of butter.
In a 12" nonstick skillet over medium heat, cook bacon until crisp, about 8 minutes. Transfer bacon to paper towels. Reserve 2 tablespoons of the bacon fat in the skillet; discard the remainder. When bacon is cool, crumble it and reserve.
In a small bowl, combine 1 tablespoons of the crumbled bacon with the breadcrumbs, 2 tablespoons of the cheese, the olive oil, 1/2 teaspoon of the thyme, and a large pinch of salt.
Add the remaining 1 tablespoons butter to the skillet with the bacon fat and melt over medium heat. Add the leeks and a pinch of salt, and cook, stirring, until softened and just starting to turn golden, 6-7 minutes. Add the garlic and stir well. Add the corn, 1/4 teaspoons of salt, and a few grinds of pepper. Cook, stirring, until the corn has lost its raw look and is slightly shrunken, 2-3 minutes. Cool slightly.
Combine cream and chicken broth in a 2 cup liquid measure. Add the lemon zest, 1/2 teaspoons salt, and a few grinds of pepper. Stir to mix well.
In a large bowl combine the remaining bacon, the corn-leek mixture, the diced squash, potatoes, and remaining 1 teaspoons thyme. Toss lightly to combine. Spread the mixture evenly in the gratin dish. Sprinkle the remaining cheese on top. Stir the cream mixture one more time and pour it over everything as evenly as possible, being sure to scrape out any seasonings from the cup. Press down on the veggies with a spatula so that the liquids surrounds them and everything is evenly distributed. Sprinkle the breadcrumb mixture evenly over all.
Cover with foil and bake 20 minutes. Remove the foil and continue to bake until the crumb topping is deeply golden and the squash and potatoes are tender when pierced with a fork, about 25 minutes. The liquid should have bubbled below the surface of the veggies, leaving browned bits around the edges of the pan. Cool for 20-25 minutes before serving.
For a main dish, try adding polish sausage.